What is an unchecked cast and how do I go about fixing it?

[Samuel Arwood]

Hi everyone. I'm back again, just now with this unchecked casting issue. I have never seen it before and all the google searches turn up code that is way beyond me. I'll post a snippet of the code giving me the problem and then the error the compiler gives me. Any help would be greatly appreciated. Thanks in advance.

private void enlargeArray( int newSize )
    {
        AnyType [] old = array;
        array = (AnyType []) new Comparable[ newSize ];
        for( int i = 0; i < old.length; i++ )
            array[ i ] = old[ i ];
    }

and during compiling i get this message:


BinaryHeap.java:76: warning: [unchecked] unchecked cast
found : java.lang.Comparable[]
required: AnyType[]
array = (AnyType []) new Comparable[ newSize ];

[Stephan van Hulst]

Yeah, this is not gonna work.

You're using a raw type in your code, which is giving you the unchecked cast problem. You normally fix this by using a fully parameterized class instead: Comparable<Whatever>. In this case it's not gonna work though, because you can't create an array of a generic type. Comparable<Whatever>[] can not be instantiated.

Anyway, I'm not really getting what the point of casting an array of Comparable to an array of AnyType is. Why not just do array = new AnyType[newSize]; ?